The conversion of carbohydrates to glycerol and other short chain polyols generally is accomplished in two stages. In the first stage a carbohydrate such as hexose is hydrogenate to produce a polyol without hydrogenolysis of the starting material carbon structure. In the second stage the polyol is subjected to hydrogenolysis conditions to produce polyols of shorter chain length.
U.S. Pat. Nos. 1,963,999; 3,935,284; and 4,380,679 describe catalytic systems for converting saccharides such as starch, glucose and fructose to hexitols such as sorbitol and mannitol.
U.S. Pat. Nos. 1,963,997; 2,335,731; 2,852,570;and 4,404,411 describe processes which utilize hydrogenolysis conditions to convert hexitols to lower polyols such as glycerol, propylene glycol and ethylene glycol.
U.S. Pat. Nos. 2,004,135; 2,209,055; 4,380,678; and 4,476,331 describe two-stage processes for hydrogenation and hydrogenolysis of carbohydrates to lower polyols such as glycerol and C.sub.2 -C.sub.3 glycols.
U.S. Pat. No. 3,965,199 describes a one-step process for converting a carbohydrate by hydrogenation and hydrogenolysis to glycerol and glycol products in the presence of a catalyst consisting of finely divided metallic nickel and tungsten oxide on a carrier.
There is continuing interest in the development of new and improved processes for efficient conversion of higher polyhydric starting materials selectively to lower polyhydric products.
Accordingly, it is an object of this invention to provide a process for converting a higher polyhydric hydrocarbon to a lower polyhydric hydrocarbon.
It is another object of this invention to provide a process for converting glycerol selectively to propanediols in a homogeneous catalytic reaction medium.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.